HR: 17:45h
AN: S54A-08    [Abstracts]
TI: Modern Seismic Observations in Tatun Volcano Group: Potential Seismic/Volcanic Hazard in Taipei Metropolitan Area of Northern Taiwan
AU: * Kim, K
EM: kim@earth.ncu.edu.tw
AF: Institute of Geophysics, National Central University, Chung-Li, 320 Taiwan
AU: * Kim, K
EM: kim@earth.ncu.edu.tw
AF: Institute of Earth Sciences, Academia Sinica, Nankang, Taipei, 115 Taiwan
AU: Chang, G
EM: gensin@ss2.cwb.gov.tw
AF: Central Weather Bureau, Kongwen-Ro 64, Taipei, 100 Taiwan
AU: Ma, K
EM: fong@earth.ncu.edu.tw
AF: Institute of Geophysics, National Central University, Chung-Li, 320 Taiwan
AU: Chiu, J
EM: chiu@ceri.memphis.edu
AF: Center for Earthquake Research and Information, The University of Memphis, Memphis, TN 38152 United States
AU: Chen, K
EM: chenkc@earth.ncu.edu.tw
AF: Institute of Earth Sciences, Academia Sinica, Nankang, Taipei, 115 Taiwan
AB: Tatun volcano group is located adjacent to the Taipei metropolitan area in northern Taiwan and was a result of episodic volcanisms between 2.8 and 0.2 Ma. Earthquake data collected over the last 30 years in different periods are analyzed to explore seismicity pattern in the area. Using JHD method, a few sequences of relocated earthquake hypocenters are tightly clustered which were somewhat blurry in the original catalog locations. Numerous new earthquakes, previously unnoticed and not reported in the CWB catalog, have been identified from a careful examination of continuous recordings from nearby seismic stations. These newly identified earthquakes show similar waveforms and similar arrival time differences between the direct P- and S-waves indicating that there are significant micro-earthquakes or swarm activities associated with hydrothermal/magmatic systems in the region. A significantly high b-value (1.22) is determined from crustal earthquakes ($<$ 30 km), which may suggest that local seismicity in the Tatun volcanic region is probably governed by subsurface hydrothermal or volcano-related structures. Focal mechanism solutions determined in this study are dominated by normal faulting. Therefore, these earthquake clusters are most probably associated with hydrothermal/magmatic structures in a back-arc extensional environment. Although there is no immediate threat of eruptive activity at the Tatun volcano region, apparent symptoms related to potential volcanic activity should be seriously considered. A long-term dense seismic array monitoring is desirable for a comprehensive study of background seismicity, regional velocity structure, attenuation of regional seismic waves, and the geometry and boundary of potential hydrothermal/magmatic structures in the region. Such study is very important for volcanic/seismic hazard assessments and for providing warning of future hazardous activity around the Taipei metropolitan area.
DE: 1734 Seismology
DE: 1749 Volcanology, geochemistry, and petrology
SC: Seismology [S]
MN: 2004 AGU Fall Meeting